1. Field of the Invention
This invention relates generally to gas turbine engines and, more particularly, to a low emission combustor assembly for an automotive gas turbine engine.
2. Description of the Prior Art
Successful commercial adaptation of a power source to automotive vehicles depends, at least in part, on the degree of success achieved in maintaining exhaust emissions of the power source within prescribed limits. Exhaust components of current primary concern are hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx) and it is known that high temperature, stoichiometric combustion is conducive to minimization of HC and CO but not to minimization of NOx while lean combustion with resulting low flame temperature is conducive to minimization of NOx but not to minimization of HC and CO. In one compromise effort relating to turbojet engines, a combustor assembly includes a pair of more or less conventional diffusion flame combustion chambers disposed in parallel, one chamber for optimum emission at engine idle and the other chamber for optimum emission at acceleration and cruise. However, because combustion chamber length requirements may conflict with vehicle space availability, this proposal lacks attractiveness for automotive applications. In another compromise effort, a combustor assembly includes a catalytic combustion chamber in series with a diffusion flame combustion chamber, the latter operating during engine start-up to directly heat the catalyst while rendering the engine self-sustaining and the former taking over for normal engine operation at low emission levels. The series arrangement, however, increases the possibility of catalyst contamination which, in automotive applications, is undesirable from a durability standpoint. A low emission combustor assembly according to this invention represents an improvement over these and other similar compromise proposals.